Mobile communications networks are in the process of offering increasingly sophisticated capabilities associated with the motion and/or position location sensing of a mobile device. New software applications, such as, for example, those related to personal productivity, collaborative communications, social networking, and/or data acquisition, may utilize motion and/or position sensors to provide new features and services to consumers. Moreover, some regulatory requirements of various jurisdictions may require a network operator to report the location of a mobile device when the mobile device places a call to an emergency service, such as a 911 call in the United States.
Such motion and/or position determination capability has conventionally been provided using both digital cellular positioning techniques and/or Satellite Positioning Systems (SPS). Additionally, with the increasing proliferation of miniaturized motion sensors (e.g., simple switches, accelerometers, angle sensors, etc), such on-board devices may be used to provide relative position, velocity, acceleration and/or orientation information.
In conventional digital cellular networks, position location capability can be provided by various time and/or phase measurement techniques. For example, in CDMA networks, one position determination approach used is Advanced Forward Link Trilateration (AFLT). Using AFLT, a mobile device may compute its position from phase measurements of pilot signals transmitted from a plurality of base stations.
Improvements to AFLT have been realized by utilizing hybrid position location techniques, where the mobile station may employ a Satellite Positioning System (SPS) receiver. The SPS receiver may provides position information independent of the information derived from the signals transmitted by the base stations. Moreover, position accuracy can be improved by combining measurements derived from both SPS and AFLT systems using conventional techniques.
However, conventional position location techniques based upon signals provided by SPS and/or cellular base stations may encounter difficulties when the mobile device is operating within a building and/or within urban environments. In such situations, signal reflection and refraction, multipath, and/or signal attenuation can significantly reduce position accuracy, and can slow the “time-to-fix” to unacceptably long time periods. These shortcomings may be overcome by having the mobile device exploit signals from other existing wireless networks, such as, for example, Wi-Fi (e.g., 801.11x standards), to derive position information. Conventional position determination techniques used in other existing wireless networks may utilize round trip time (RTT) measurements derived from signals utilized within these networks.
Utilizing RTT measurement techniques to accurately determine position typically involves knowledge of time delays incurred by the wireless signals as they propagate through various devices comprising the network. Such delays may be spatially variant due to, for example, multipath and/or signal interference. Moreover, such processing delays may change over time based upon the type of network device and/or the network device's current networking load. In practice, when employing conventional RTT positioning techniques, estimating processing delay times may involve hardware changes in the wireless access points, and/or time-consuming pre-deployment fingerprinting and/or calibration of the operational environment.
Accordingly, when using RTT techniques for position determination, it may be desirable to exploit on-board relative motion sensors to assist in the estimation of processing delays. Such techniques may improve the position location accuracy and performance a mobile device in a cost-efficient manner.